This invention relates to belt drives, and more specifically to variable pitch diameter torque sensing pulley assemblies used in V-belt drives.
In both flat belt and V-belt drives, one of the factors which influence the torque which the drive can transmit is belt slippage. That is, relative movement between the belt and the pulley around which it is reeved. Concerning V-belt drives, belt slippage, and hence torque transmission depends upon, inter alia, the axial loading being exerted upon the sides of the V-belt. This presents a problem because as axial loading goes up on a V-belt, its life goes down. In order to solve this problem, belt drives having pulley assemblies which automatically vary the axial loading on the V-belt in response to torque transmission have been developed. In fact, there are even variable pitch diameter torque sensing pulley assemblies which are used in variable speed V-belt drives. An example of such a pulley assembly and drive is shown in U.S. Pat. No. 4,173,155 issued in the name of P. G. Togami et al. on Nov. 6, 1979.
However, pulley assemblies of the single cam set type shown in U.S. Pat. No. 4,173,155 have a shortcoming. In order to accommodate the axial displacement of the pulley halves to provide a variable pitch diameter, the cam surfaces have to be relatively long, especially when the slope of the cam surface is low. As a result, the number of cams in a cam set that can be provided in such a pulley assembly is limited to a small number. This is undesirable because the torque being transmitted by the pulley assembly will have to be transmitted through a small number of cams and cam followers. Also, since the cam surfaces are long, substantial twisting forces will be imposed upon the cam set member due to torque transmission by the pulley assembly.
My improved pulley assembly overcomes the shortcoming described above by providing a cam follower which cooperates with a pair of cam sets with different slopes selected so that when the pulley assembly is adjusted between the minimum and an intermediate pitch diameter, a relatively high axial loading is imposed on the V-belt, and when the pulley assembly is adjusted between the intermediate and the maximum pitch diameter, a relatively low axial loading is imposed upon the V-belt. This not only provides for lower axial loading on the V-belt when the pulley assembly is adjusted for large pitch diameters, but also permits the cam surfaces to be shorter so that more cams can be included in a cam set and lowers the twisting forces on the cam set member due to torque transmission.